Dense ceramic bars of the perovskite material SrFe0.8Co0.2O3-delta have been synthesized by solid-state reaction and studied by in-situ neutron diffraction through the range of oxygen partial pressure (pO(2)) from 10 (-0.68) to 10 (-13.3) atm at 900 degreesC. Over the complete range, the material retains the cubic perovskite structure and is stable even when delta>0.5. Between air and log pO(2) = -2.3, delta increases from 0.35 to 0.44 and the lattice expands. Lowering the pO(2) further leads to an oxygen content "plateau" at delta approximate to 0.5, through a log pO(2) range of - 3.5 to - 8.6. Below this, the lattice undergoes further expansion, as oxygen is lost, most likely when Co3+ undergoes reduction to Co2+. Rietveld analysis indicates that there is no deviation from the Fe/Co 80:20 ratio over the entire pO(2) range. The behavior of this perovskite is compared to that of the perovskite phase of similar composition found in a SrFeCo0.5Oy ceramic membrane material studied under similar conditions.